1. Field of the Invention
This invention pertains to an improved multiple zone coal conversion process for producing fuel gas and distillate liquids, and particularly to such a coal conversion process wherein coal is devolatilized in an upper bed of particulate carrier material which is used to facilitate the gasification of adsorbed coke in a lower combustion zone.
2. Description of Prior Art
Considerable work has previously been done for the multi-stage gasification of heavy oil feeds in fluidized beds, some processes using a particulate carrier material for deposition of carbon, and for the multiple stage gasification of coal. Some typical pertinent patents include U.S. Pat. No. 2,861,943 to Finneran which teaches the use of a circulating particulate carrier for coke laydown from a residual oil feedstock, but does not teach use of such carrier material for tar deposition from coal gasification processes in which the tar is formed within the process. U.S. Pat. No. 3,202,603 to Keith teaches a multiple bed hydro-gasification process for residual oils and tar feeds and using a particulate carrier material for hydrocracking the heavy oil feed to produce gas and liquid fractions. But no mention is made of removing tars, particularly from coal feeds.
U.S. Pat. No. 3,953,180 to Hoffert discloses a gasification process for petroleum residuum feedstocks, which utilizes a heat exchange step in an upper fluidized bed to cool the product gas stream before use as gas turbine fuel. However, no mention is made of gasification of coal or the deposition of tars on a circulating carrier material.
U.S. Pat. No. 3,817,732 to Donath teaches two-stage gasification of coal in separate reactors, but does not utilize a circulating particulate contact material for removal of tars from product gas. U.S. Pat. No. 3,847,563 to Archer teaches a multiple stage gasification process for coal which uses a fluidized bed of limestone (CaO) or dolomite to absorb sulfur from the gas generated. Also, two separate reactor vessels are used instead of a single vessel having multiple reaction zones.
U.S. Pat. No. 4,099,933 to Johnson describes a multiple zone gasification process for coal designed to prevent carryover of tars with the product gas stream by using staged beds of coal at increasing temperature levels. However, a particulate carrier material is not used for deposition of such tars.
There has thus been an unfulfilled need for a practical coal conversion and gasification process to produce fuel gas and distillable liquids, which would also effectively react tars evolved from the coal and produce clean fuel gas and liquid products.